The present invention relates to a recording medium and a process for preparing the same. More specifically, the present invention relates to a recording medium, in which the surface strength of the coating surface is strong, ink blurring when printing hardly occurs, particularly when used for ink jet printing, and water resistance after printing is excellent, and a process for preparing the same.
In a recording medium in which a coating layer is formed on a substrate such as paper or resin film, often a coating layer containing inorganic powder is formed with the purpose of improving ink absorbency and whiteness. Examples of such recording mediums are a heat sensitive recording medium, to which recording is conducted by color developing a coloring substance such as crystal violet lactone and a developer such as a phenol compound by heat reaction, and a recording medium for ink jet printing, to which recording of symbols is conducted by spraying ink droplets from a nozzle and adhering and absorbing the ink to the surface of a substrate such as paper or resin film.
Particularly in recent years, the ink jet printing method is widely used in various printers because of the advantages of high-speed printing, multi-color printing and less sound when printing. With respect to the recording medium used for the ink jet printing method, improvement in coloring properties of the printing side and properties such as glossiness for providing high-quality appearance and ink absorbency for preventing stickiness of the printed area are in demand.
As a method to satisfy such demands, JP-A-62-158084 discloses a method of using a recording medium for ink jet printing having an ink receiving layer comprising fine particle silica as a main component and a recording surface which is dried by pressure welding to a heated mirror surface.
Also, the present applicant has suggested a recording medium for ink jet printing containing polyvinyl alcohol resin, titanate coupling agent and inorganic powder in the coating layer in order to improve the surface strength of the coating layer (ink receiving layer) (see JP-A-2001-328345) and a paper processing agent using polyvinyl alcohol resin having an acetoacetic ester group and zirconium salt in order to improve stiffness of paper (see JP-A-1-156597).
When using for ink jet printing, attempts have been made to add inorganic powder in the ink receiving layer, as in JP-A-62-158084 and JP-A-2001-328345. However, in order to improve ink absorbing speed and absorbing capacity, which are functions of inorganic powder, adjustments must be made such as reducing the amount of the binder. As a result, there is the problem of decrease in surface strength of the ink receiving layer.
Therefore, as in the art disclosed in JP-A-62-158084, by merely conducting mirror treatment to the surface, the surface strength of the ink receiving layer is still weak and there is the problem that during the process of preparing the recording medium, particularly when cutting, powder, which has partially peeled off and fallen from the ink receiving layer, or powder, which has fallen when printing, adheres to the nozzle causing clogging. Also, recently printing of images such as photographs is increasing and the problem of ink blurring when conducting this type of printing has newly arisen. Furthermore, when used as label for food packaging, in the case of strong contact in the presence of water, the printed area (ink receiving layer) may become damaged or peel off and problems may arise with respect to water resistance of the ink receiving layer. The art disclosed in JP-A-62-158084 has been found to be insufficient regarding this point.
Also, in art disclosed in JP-A-2001-328345, although some improvement in surface strength of the ink receiving layer can be expected, there is room for improvement with respect to ink blurring when printing and water resistance of the ink receiving layer after printing, as in the art disclosed in JP-A-62-158084.
The art disclosed in JP-A-1-156597 is excellent in surface strength of the coating layer but ink absorbency is insufficient, as inorganic powder is not used.
Consequently, not only excellent surface strength of the ink receiving layer, but also favorable ink absorbency, ink blurring prevention when printing and improved water resistance of the ink receiving layer after printing are desired.